Amorphous silica or silica-alumina spherical particles and process for preparation thereof

ABSTRACT

Disclosed are amorphous silica or silica-alumina spherical particles composed of X-ray diffractometrically substantially amorphous silica or silica-alumina, wherein individual particles have a definite spherical shape and a notched surface, the circularity (A) represented by the following formula: ##EQU1## wherein r1 stands for the radius of the circumcircle of the profile of the particle in an electron microscope photo thereof and r2 stands for the radius of the inscribed circle of the profile of the particle in the electron microscope photo, is in the range of from 0.90 to 1, the notching degree (B) represented by the formula: ##EQU2## wherein Δt stands for the depth between the peak and trough in the radial direction of notches on the profile of the particle in the electron microscope photo and r1 is as defined above, is in the range of from 1 to 10%, and the primary particle size (2r1) determined by the electron microscope method is in the range of from 0.1 to 20 μm.

This is a division of application Ser. No. 07/956,421, filed on Oct. 2,1992, now U.S. Pat. No. 5,236,683, which is a file-wrapper continuationapplication of Ser. No. 07/825,427, filed on Jan. 22, 1992, nowabandoned, which is a file-wrapper continuation application of Ser. No.07/698,251, filed on May 6, 1991, now abandoned, which is a file-wrappercontinuation application of Ser. No. 07/145,586, filed on Jan. 19, 1988,now abandoned.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to amorphous silica or silica-aluminaspherical particles having a novel particulate shape and a process forthe preparation thereof.

(2) Description of the Prior Art

Spherical particles of amorphous silica or silica-alumina are widelyused as fillers for various films and other resins and rubbers, asfillers for cosmetics, as supporting carriers for perfumes andchemicals, as chromatography filler and for other purposes.

Spherical amorphous silica has been prepared according to the process inwhich a silica hydrosol is sprayed or the spray is further caused toimpinge to a fluid, the process in which an organic silicic acidcompound is hydrolyzed, the process in which a glass ceramic is moldedinto a spherical shape and is sintered, and the like process.

However, silica or silica-alumina spherical particles prepared accordingto these processes have a relatively coarse primary particle size and abroad particle size distribution. Therefore, development of silica orsilica-alumina spherical particles having a fine primary particle sizeand a sharp particle size distribution is eagerly desired in the art.

When such spherical particles are used as a filler for a resin, thedispersibility of the particles in the resin and the compatibility ofthe particles with the resin should be taken into consideration. Forexample, when a resin having spherical particles incorporated therein isformed into a film or the like and is then drawn, a problem of formationof voids between the resin and the filler particles often arises.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provideamorphous silica or silica-alumina particles having a novel particulateshape, in which the primary particle size is fine, the particles have adefinite spherical shape and the particles have a notched surface, and aprocess for the preparation of these particles.

Another object of the present invention is to provide amorphous silicaor silica-alumina particles which are excellent in the dispersibility inresins and the compatibility with resins and in which formation of voidsbetween the particles and resins is prevented at various processingsteps.

Still another object of the present invention is to provide amorphoussilica or silica-alumina particles which have an excellent supportingproperty for various chemicals, perfumes and the like because of notchesformed on the surfaces thereof.

In accordance with one aspect of the present invention, there areprovided amorphous silica or silica-alumina spherical particles composedof X-ray diffractometrically substantially amorphous silica orsilica-alumina, wherein individual particles have a definite sphericalshape and a notched surface, the circularity (A) represented by thefollowing formula: ##EQU3## wherein r1 stands for the radius of thecircumcircle of the profile of the particle in an electron microscopephoto thereof and r2 stands for the radius of the inscribed circle ofthe profile of the particle in the electron microscope photo, in therange of from 0.90 to 1, the notching degree (B) represented by thefollowing formula: ##EQU4## wherein Δt stands for the depth between thepeak and trough in the radical direction of notches on the profile ofthe particle in the electron microscope photo and r1 is as definedabove,

is in the range of from 1 to 10%, and the primary particle size (2r1)determined by the electron microscope method is in the range of from 0.1to 20 μm.

In accordance with another aspect of the present invention, there isprovided a process for the preparation of amorphous silica orsilica-alumina spherical particles, which comprises the step ofsynthesizing zeolite particles having an X-ray diffraction patterninherent to P type zeolite, individual particles having a definitespherical shape as a whole and a notched surface, and the step ofsubjecting the zeolite particles to a one-staged or multiple-staged acidtreatment to remove the sodium component or the sodium and aluminacomponents sufficiently to render the zeolite amorphous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 are electron microscope photos of silica particles,silica-alumina particles and particles of starting P type zeolite,respective.

FIGS. 4, 5 and 6 are X-ray diffraction patterns of amorphous silicaparticles, amorphous silica-alumina particles and P type zeoliteparticles, respectively.

FIG. 7 shows the section of the projection of the peripheral profile ofthe particle according to the electron microscope method, in which r1stands for the radius of the circumcircle 1, r2 stands for the radius ofthe inscribed circle 2 and reference numerals 3 and 4 represent the peakand trough in the radial direction of notches on the peripheral profileof the particle.

FIG. 8 is a histogram of the particle size distribution of sphericalsilica particles.

FIGS. 9, 10 and 11 are electron microscope photos of spherical particleshaving particle sizes of 1.2 um, 6.0 um, and 0.8 um, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

We succeeded in synthesizing zeolite particles having an X-raydiffraction pattern inherent to P type zeolite and having a definitespherical shape as a whole and a notched surface, and we found that ifsuch zeolite particles are subjected to an acid treatment to remove thesodium component or the sodium and alumina components, sphericalparticles of amorphous silica or silica-alumina can be obtained.

The spherical particles of amorphous silica or silica-alumina accordingto the present invention are prominently characterized in that althoughthe particles are composed of amorphous silica or silica-alumina, theparticles have a definite spherical shape and the surfaces of thespherical particles are notched.

FIG. 1 of the accompanying drawing is an electron microscope photo(10,000 magnifications) of amorphous silica particles of the presentinvention. FIG. 2 is an electron microscope photo (10,000magnifications) of amorphous silica-alumina particles of the presentinvention. FIG. 3 is an electron microscope photo (10,000magnifications) of P type zeolite particles (used as the startingmaterial).

From these electron microscope photos, surprising characteristicfeatures of the present invention are understood. That is, it is seenthat the spherical particles of amorphous silica or silica-aluminaaccording to the present invention have a spherical shape resembling thetrue sphere as a whole as well as P type zeolite and they have a notchedsurface.

FIG. 4 shows an X-ray diffraction pattern (Cu-α) of the sphericalamorphous silica particles shown in FIG. 1, FIG. 5 shows an X-raydiffraction pattern of the spherical amorphous silica-alumina particlesshown in FIG. 2, and FIG. 6 shows an X-ray diffraction pattern of the Ptype zeolite particles shown in FIG. 3. From these X-ray diffractionpatterns, it is seen that the product of the present invention has aparticulate structure similar to that of the P type zeolite particles,but the product of the present invention is X-ray diffractometricallyamorphous and is different from the P type zeolite particles in thispoint.

In FIG. 7 illustrating the circularity (A) and notching degree (B)mentioned in the instant specification, the section of the projection ofthe peripheral profile of the particle according to the electronmicroscope method is shown. The circumcircle 1 and inscribed circle 2 ofthis peripheral profile are drawn, and the circularity (A) is determinedfrom the radius r1 of the circumcircle 1 and the radius r2 of theinscribed circle 2 according to the formula (1). This circularity (A)has the following meaning. Namely, in case of the true circle, since r1is equal to r2, the circularity (A) is 1, and as the peripheral profileof the particle is deviated from the true circle, the difference betweenr1 and r2 is increased and the circularity (A) is smaller than 1. Thenotching degree (B) is determined from the depth Δt between the peak andtrough in the radial direction of the notched profile of the particleaccording to the formula (2). This notching degree (B) is a valueindicating the notch roughness of the surface.

In the particles of the present invention, the circularity (A) is in therange of from 0.90 to 1.0, especially from 0.95 to 1.0, and the notchingdegree (B) is in the range of from 1 to 10%, especially from 1.5 to 5%.This is another characteristic feature of the particles of the presentinvention. If the circularity (A) is too small and the below theabove-mentioned range, the characteristics of spherical particles, suchas good flowability and high bulk density, are lost and thedispersibility in resins or the like are degraded. The notching degree(B) has great influences on the interfacial properties between theparticles and other substance when the particles are used in variousfields. For example, when the particles of the present invention areincorporated into a resin and the composition is molded, since the resinis tightly engaged with the particles through the notched surfacesthereof, even if the molded film or the like is subjected to a drawingoperation, formation of voids is controlled and a film excellent in thetransparency can be obtained. If the notching degree (B) is too low andbelow the above-mentioned range, the compatibility with resins isdegraded, and if the notching degree (B) exceeds the above-mentionedrange, the strength of the particles per se is reduced or wearing of anapparatus or member falling in contact with the particles is increased.Moreover, if the notching degree (B) is within the above-mentionedrange, when the particles are used as a carrier for agriculturalchemicals or other chemicals, the supporting capacity is advantageouslyincreased. This advantage is similarly attained when the sphericalparticles of amorphous silica or silica-alumina according to the presentinvention are used as a chromatography adsorbent.

In the spherical particles of amorphous silica or silica-aluminaaccording to the present invention, the primary particle size (theparticle size according to the electron microscope photo method, thatis, 2r1) is in the range of from 0.1 to 20 μm, especially from 0.3 to 10μm. Namely, the amorphous silica or silica-alumina particles of thepresent invention are characterized in that although individualparticles have a definite spherical shape, the primary particle size isrelatively small within the above-mentioned range. If the primaryparticle size is too small and below the above-mentioned range,secondary aggregation is readily caused and no good results can beobtained. If the primary particle size exceeds the above-mentionedrange, the particles are not suitable as a resin filler.

The amorphous silica or silica-alumina of the present invention can beused either in the state where the primary particle size is very uniformand the particle size distribution is very sharp, or in the state wherethe primary particle size is distributed in a broad range, according tothe intended object. In the former case, the standard deviation of theprimary particle size in the spherical particles can be less than 0.85,especially less than 0.5.

The spherical particles of amorphous silica or silica-alumina accordingto the present invention are relatively dense, and the bulk density isgenerally in the range of from 0.2 to 1.2 g/ml and especially in therange of from 0.4 to 1.0 g/ml, though the bulk density differs to someextent according to the particle size. The BET specific surface of thespherical particles is smaller than 400 m² /g, especially smaller than300 m² /g, though the BET surface area differs to some extent accordingto the particle size or the notching degree (B) of the surface.

The amorphous silica or silica-alumina of the present invention has thefollowing composition by weight, though the composition differs to someextent according to the preparation process.

    ______________________________________                                                  General Range                                                                           Preferred Range                                           ______________________________________                                        SiO.sub.2     60 to 99.99%                                                                              70 to 99.99%                                        Al.sub.2 O.sub.3                                                                           0 to 25%    0 to 15%                                             Na.sub.2 O   0 to 12%   0 to 4%                                               ignition loss                                                                             below 15%   below 13%                                             ______________________________________                                    

When the spherical particles of the present invention are formed into anaqueous dispersion having a solid concentration of 1% by weight, thedispersion shows a pH value of 4.0 to 10, and this pH value is smallerthan the pH value of the dispersion of the starting zeolite, which islarger than 11.

In accordance with one preferred embodiment of the present invention,there are provided amorphous silica-alumina spherical particles composedof X-ray diffractometrically substantially amorphous silica-aluminahaving an SiO₂ /Al₂ O₃ molar ratio of from 6 to 30 and an Na₂ O contentlower than 2.0% by weight, wherein when the particles are held in anatmosphere maintained at a temperature of 25° C. and a relative humidityof 90% for 24 hours, the moisture absorption is lower than 13%. Sincethe particles of this type have a very low moisture absorption, when theparticles are incorporated into a resin or rubber, blowing is controlledunder processing conditions, and therefore, the particles are especiallyvaluable as a filler for polymers.

In accordance with another preferred embodiment of the presentinvention, there are provided amorphous silica spherical particlescomposed of X-ray diffractometrically substantially amorphous silicahaving an SiO₂ content of at least 85% by weight, wherein when theparticles are held in an atmosphere maintained at a temperature of 25°C. and a relative humidity of 90% for 24 hours, the moisture absorptionis in the range of 5 to 25% by weight. Since the particles of this typehave a higher moisture absorption and a higher surface activity thanthose of the above-mentioned amorphous silica-alumina sphericalparticles, the particles are especially valuable as a filler forcosmetics.

For this production of the amorphous silica or silica-alumina sphericalparticles of the present invention, at first, zeolite particles havingan X-ray diffraction pattern inherent to P type zeolite, in whichindividual particles have a definite spherical shape as a whole and anotched surface, are prepared.

Of course, P type zeolite particles having a spherical shape are know.In the conventional synthesis processes, P type zeolite is formed as aby-product when X type zeolite and Y type zeolite are synthesized, andthere is not known a process in which only P type zeolite in the form ofspherical particles is efficiently synthesized.

We found that P type zeolite can be synthesized by mixing sodiumsilicate or active silicic acid gel, sodium aluminate and sodiumhydroxide under the following molar ratio conditions to form a gel of analkali metal alumino-silicate, homogenizing this gel and effectingcrystallization at a temperature of 85° to 200° C. under atmosphericpressure or under hydrothermal conditions. P type Zeolite-FormingRatios:

    ______________________________________                                        Component   Ordinary Molar                                                                            Preferred Molar                                       Ratio       Ratio       Ratio                                                 ______________________________________                                        Na.sub.2 O/SiO                                                                            0.2 to 8    0.5 to 2.0                                            SiO.sub.2 /Al.sub.2 O.sub.3                                                                3 to 20     4 to 10                                              H.sub.2 O/Na.sub.2 O                                                                       20 to 200   30 to 100                                            ______________________________________                                    

The formed zeolite is washed with water, the classifying operation iscarried out so that a desired particle size is obtained, and the zeoliteis then subjected to an acid treatment described below.

In the present invention, in order to prepare amorphous silica orsilica-alumina particles having a high circularity (A), it is preferredthat P type zeolite be used as the starting material. The chemicalcomposition of this starting P type zeolite is as follows.

Chemical Compositions of P Type Zeolite

SiO₂ : 40 to 70% by weight

Al₂ O₃ : 15 to 30% by weight

Na₂ O: 8 to 20% by weight

H₂ O: 0 to 20% by weight

From the above chemical composition, it is seen that the startingzeolite used in the present invention is advantageous in that since theSiO₂ /Al₂ O₃ ratio is high, the amount of the Al₂ O₃ component to beremoved is small.

According to the present invention, the above-mentioned zeoliteparticles are subjected to a one-staged or multiple-staged acidtreatment to remove the sodium component or the sodium and aluminacomponents sufficiently to render the zeolite amorphous. It was foundthat if at least 0.3 mole %, especially at least 0.5 mole %, of the Na₂O component is removed in P type zeolite, the particles are renderedX-ray diffractometrically amorphous. Accordingly, if the sodiumcomponent is removed in an amount exceeding the above-mentioned lowerlimit, spherical silica-alumina particles can be obtained, and if thealumina component is further removed by the acid treatment, sphericalsilica particles can be obtained.

Either an inorganic acid or an organic acid can be used for the acidtreatment without any limitation. From the economical viewpoint, use ofa mineral acid such as hydrochloric acid, sulfuric acid, nitric acid orphosphoric acid is preferred. The acid is preferably used in the form ofan aqueous solution for neutralization of the zeolite or elution of thealumina component.

It is preferred that the acid treatment be performed by forming anaqueous slurry of the crystalline zeolite and adding the acid to theslurry. As the acid is added, the pH value is shifted to the acidicside, and as the neutralization is advanced, the pH value is shifted tothe alkaline side again and the pH value becomes saturated. It ispreferred that the neutralization be effected so that the saturated pHvalue is 2.0 to 7.0, especially 3.5 to 7.0. If this saturated pH valueexceeds the above-mentioned range, it is difficult to remove the alkalicomponent from the zeolite so that the zeolite is rendered amorphous. Ifthe saturated pH value is below the above-mentioned range, it isdifficult to perform the acid treatment while maintaining thepredetermined shape in the formed particles. As regards other acidtreatment conditions, it is preferred that the temperature be 20° C. to100° C., and the concentration of the zeolite particles in the slurry ispreferably 5 to 30% by weight.

The acid treatment may be conducted in one stage or two or more stages.For example, in the case where only the sodium component is removed, aone-staged treatment is sufficient, and in the case where the aluminacomponent is removed as well as the sodium component, a multiple-stagedtreatment such as a two- or three-stage treatment is effective. In thelatter case, there is preferably adopted a method in which the sodiumcomponent in the zeolite is removed by the first heat treatment and theacid-treated product is dried or calcined and then subjected to thesubsequent heat treatment to remove at least a part of the aluminacomponent. The intermediate drying or calcining treatment is performedso as to prevent disintegration of the particles at the subsequent heattreatment. It is considered that this effect is due to the shrinkage ofthe particles caused by drying or calcining.

The obtained amorphous silica or silica-alumina spherical particles arewashed with water, dried and calcined to obtain a final product.

When the water absorption is measured after the particles are held in anamorphous maintained at a temperature of 25° C. and a relative humidityof 90% for 24 hours, the water absorption of starting P type zeolite is20 to 25% by weight, which is a level inherent to the zeolite. Incontrast, the water absorption, determined under the same conditions, ofthe amorphous silica-alumina of the present invention is smaller 13% byweight, and the water absorption of the silica of the present intentionis 5 to 25% by weight. This means that when the spherical particles ofthe present invention are incorporated into various resins, especiallythermoplastic resins, blowing owing to absorbed water is controlled atthe molding step and also in this point, the spherical particles of thepresent invention are advantageous as a resin filler.

The spherical particles of the present invention are preferablysurface-treated or surface-coated with metal soaps, resin acid soaps,resins or waxes, silane or titanium type coupling agents or silicaaccording to need.

The amorphous silica or silica-alumina spherical particles of thepresent invention can be incorporated in various resins, for example,olefin resins such as polypropylene, polyethylene, a crystallinepropylene/ethylene copolymer, an ion-crosslinked olefin copolymer and anethylene/vinyl acetate copolymer, thermoplastic polyesters such aspolyethylene terephthalate and polybutylene terephthalate, polyamidessuch as 6-nylon and 6,6-nylon, chlorine-containing resins such as avinyl chloride resin and a vinylidene chloride resin, polycarbonates,polysulfones and polyacetals, and a good slipping property oranti-blocking property can be imparted to molded articles of theseresins, for example, biaxially drawn films.

Furthermore, the spherical particles of the present invention can beused as a filler or reinforcer for molding thermosetting resins orcoating-forming paints or as a ceramic substrate.

Moreover, the spherical particles of the present invention can be usedas an inorganic filler for an electroviscous liquid comprising anelectroconductive oil and an inorganic dispersed substance, which isused for a clutch, a hydraulic pressure valve, a shock-absorbing systemand the like.

Still in addition, the spherical particles of the present invention arevaluable as carriers for supporting cosmetic bases such as powderfoundation, liquid (paste) foundation, baby powder and cream, medicines,agricultural chemical, perfumes, aromatic agents and the like, and canbe used as a carrier for various chromatographies.

The present invention will now be described in detail with reference tothe following examples that by no means limit the scope of theinvention.

EXAMPLE 1

By using commercially available water glass of the reagent grade (sodiumsilicate No. 3, SiO₂ =27% by weight, Na₂ =9.0% by weight), sodiumaluminate (Al₂ O₃ =22.5% by weight, Na₂ O=15.5% by weight) and causticsoda, a dilute solution of sodium silicate and a solution of sodiumaluminate were prepared so that the entire amount was 16 kg and thefollowing molar ratios were attained:

Na₂ O/SiO₂ =0.7,

SiO₂ /Al₂ O₃ =8.8, and

H₂ O/Na₂ O=80.

In a stainless steel vessel having an inner volume of about 25 l, 8.3 kgof the aqueous solution of sodium silicate was gradually mixed with 7.8kg of the dilute solution of sodium aluminate with stirring to form anentirely homogeneous gel of sodium aluminosilicate. Then, thetemperature of the sodium aluminosilicate gel was elevated to 90° C.with violet stirring and at this temperature, crystallization waseffected over a period of 48 hours.

Then, the solid was separated from the mother liquor by suctionfiltration and the solid was sufficiently washed with water to obtainabout 1.7 kg of a P type zeolite cake having a solid concentration of43% by weight. Water was added to the cake so that the solidconcentration was 10% by weight, and the solid was sufficientlydispersed. Classification was repeated several times by using a smallliquid cyclone to from a starting material to be subjected to the firststage acid treatment. The so-obtained slurry was dried in an ovenmaintained at 80° C. for 24 hours. The electron microscope photo of thedried product is shown in FIG. 3 and an X-ray diffraction pattern of thedried product is shown in FIG. 6. Furthermore, the properties andchemical composition of the obtained powder (sample 1-1) are shown inTable 1. Then 3 l of the wet-classified slurry was charged in a beakerhaving an inner volume of 5 l, and about 1.3 l of dilute sulfuric aciddiluted to a concentration of 10% by weight was gradually added withstirring. After the addition, the mixture was stirred for 1 hour and thesolid was separated from the mother liquor by suction filtration. Thesolid was sufficiently washed with water and the cake was dried in andelectric thermostat drier maintained at 80° C. for 24 hours. The X-raydiffraction pattern of the dried product is shown in FIG. 2. Theproperties and chemical composition of the powder (sample 1-2 ) areshown in Table 1. Then, about 300 g of the dried powder was calcined at450° C. for 2 hours and naturally cooled. Then, 200 g of the calcinedpowder was charged in a beaker having an inner volume of 2 l, and 1,200ml of water was added thereto and the mixture was stirred and dispersedfor 30 minutes by a magnetic stirrer.

Then 110 or 270 ml of sulfuric acid of the reagent grade diluted to 50%by weight, this amount being 2 or 5 moles per mole of the sum of Al₂ O₃and Na₂ O in the powder, was gradually added to the dispersion. At thispoint, the temperature was elevated to about 90° C. Stirring wasconducted for 30 minutes after the addition of sulfuric acid, and thetemperature was gradually elevated and the treatment was carried out at98° C. for 2 hours.

The solid was separated from the mother liquor by suction filtration,and the solid was sufficiently washed with pure water in an amount 5times the amount of the mother liquor to obtain a cake of sphericalsilica particles. Then, the cake was dried in an electric thermostatdrier maintained at 110° C. for 24 hours and pulverized according tocustomary procedures using a sample mill to obtain a powder of sphericalsilica particles. The properties and chemical composition of theso-obtained powder (sample 1-3 or 1-4) are shown in Table 1.

An electron microscope photo of the powder (sample 1-4) aftercalcination at 450° C. for 2 hours was taken, and the sizes of 100particles in the photo were measured. The obtained particle sizedistribution is shown in FIG. 10. The standard deviation (σ) was 0.418.A typical electron microscope photo of the particles is shown in FIG. 1.From these photos, the circularity (A) was determined according to thefollowing formula with respect to 5 points: ##EQU5## wherein r1 standsfor the radius (μm) of the circumcircle and r2 stands for the radius(μm) of the inscribed circle.

The obtained results are shown in Table 2.

Furthermore, from the electron microscope photos, the notching degree(B) was determined according to the following formula with respect to 5points: ##EQU6## wherein Δt stands for the depth (μm) between the peakand trough on the periphery and r1 stands for the radius (μm) of thecircumcircle.

The obtained results are shown in Table 2.

Measurement Methods

In the examples, (1) the pack density, (2) the specific surface area,(3) the oil absorption, (4) the whiteness, (5) the pH value, (6) theparticle size by an electron microscope, (7) the X-ray diffractometry,(8) the chemical composition, (9) the moisture absorption and (10) theaverage particle size were determined according to the followingmethods.

(1) Pack Density

The pack density was determined according to the method of JIK K-66206-8.

(2) Specific Surface Area

The specific surface area was measured by the BET method usingSorptomatic Series 1800 supplied by Caeroeruba Co.

(3) Oil Absorption

The oil absorption was determined according to the method of JIS P-8123.

(4) Whiteness

The whiteness was determined according to the method of JIS P-8123.

(5) pH Value

The pH value was measured according to the method of JIS K-5101 24A.

(6) Particle Size by Electron Microscope

An appropriate amount of a sample fine powder was placed on a metalsheet and was sufficiently dispersed, and the powder was metal-coated bya metal coating apparatus (Ion Sputter Model E-101 supplied by Hitachi)to obtain a sample to be photographed. Several electron microscopephotographic images were obtained while changing the visual fieldaccording to customary procedures using a scanning type electronmicroscope (Model S-570 supplied by Hitachi). A typical particle imagewas selected among the spherical particle images of each visual fieldand the diameter of the spherical particle image was measured andindicated as the primary particle size in the instant specification.

(7) X-ray Diffractometry

A sample was first passed through a 200-mesh Tyler standard sieve anddried in an electric thermostat drier maintained at 80° C. for 5 hours.Then, the sample was naturally cooled in a desiccator and the X-raydiffractometry was carried out under the following conditions toidentify the crystal form.

Apparatus

X-ray diffraction apparatus supplied by Rigaku Denki, provided withgoniometer PMG-S2 and rate meter ECP-D2.

Measurement Conditions

Target: Cu

Filter: Ni

Voltage: 35 kV

Current: 20 mA

Full scale of counting: 4×10³ C/S

Time constant: 1 second

Chart speed: 1 cm/min

Scanning speed: 1°/min

Diffraction angle: 1°

Slit width: 0.15 mm

Measurement range: 2θ=5° to 40°

(8) Chemical Composition

The ignition loss (Ig-loss), silicon dioxide (SiO₂), aluminum oxide (Al₂O₃) and sodium oxide (Na₂ O) were determined according to the method ofJIS M-8852. When the contents of aluminum oxide and sodium oxide weretraces, the atomic adsorption spectroscopy method was adopted incombination.

(9) Moisture Absorption

A weighting bottle of 40 mm×40 mm, the weight of which had beenmeasured, was charged with about 1 g of the sample, and the sample wasdried in an electric thermostat drier maintained at 150° C. for 3 hoursand was then naturally cooled in a deciccator. Then, the weight of thesample was precisely measured and was charged in a disiccator, therelative humidity of which had been adjusted to 90% in advance withsulfuric acid. The weight increase after 24 hours was measured and thisweight increase was designated as the moisture absorption.

(10) Average Particle Size

Precisely weighed 1 g of the sample was charged in a beaker having aninner volume of 200 ml, and 150 ml of deionized water was added thereto.The sample was dispersed with stirring under ultrasonic vibration. Theaccumulated particle size distribution was determined by a Coltercounter (Model TAII) and an aperture tube 50μ, and the average particlesize was determined from the accumulated particle size distributiondiagram.

                                      TABLE 1                                     __________________________________________________________________________    Sample No.           1-1  1-2   1-3   1-4                                     __________________________________________________________________________    Pack density (g/ml)  0.77 0.76  0.79  0.81                                    Specific surface area (BET method) (m.sup.2 /g)                                                    --   31    195   283                                     Oil absorption (ml/100 g)                                                                          46   46    48    58                                      Whiteness (Hunter reflection method) (%)                                                           96.6 96.5  96.4  96.8                                    pH Value of 5% suspension (-/25° C.)                                                        10.9 8.9   7.8   4.8                                     Particle size (μm) by electron microscope                                                       4.5, truly                                                                         4.0, truly                                                                          4.0, truly                                                                          3.8, truly                                                   spherical                                                                          spherical                                                                           spherical                                                                           spherical                               Crystal form by X-ray diffractometry                                                               Pc form                                                                            amorphous                                                                           amorphous                                                                           amorphous                               Chemical Composition (% by weight)                                            (based on product dried at 110° C.)                                    Ig-loss              11.77                                                                              9.51  9.32  7.38                                    SiO.sub.2            51.88                                                                              56.72 76.5  92.46                                   Al.sub.2 O.sub.3     22.66                                                                              24.95 10.2  0.18                                    Na.sub.2 O           13.60                                                                              8.76  3.70  0.0                                     Total                99.91                                                                              99.94 99.72 100.03                                  SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio                                                            3.89 3.86  7.5   8.73                                    Moisture absorption (% by weight)                                                                  19.1(12.5)                                                                         9.6(4.3)                                                                            9.8(5.1)                                                                            22.7(14.6)                              (90% RH × 24 hours)*1                                                   Yield (%)*2          100  93.6  88.2  63.2                                    Average particle size (D.sub.50) (μm)                                                           4.7  4.3   4.1   3.9                                     __________________________________________________________________________     Note                                                                          *1: the parenthesized value indicates the moisture absorption of powder       calcined at 500° C. for 1 hour                                         *2: the yield was calculated from the amount of obtained powder as the        anhydride                                                                

                                      TABLE 2                                     __________________________________________________________________________            Radius r2 (mm)                                                                        Depth Δt (mm)                                           Radius r1 (mm)                                                                        of inscribed                                                                          between peak                                                                          Circularity                                                                         Notching                                        of circumcircle                                                                       circle  and through                                                                           (A)   degree (B)                                                                          Remarks                                   __________________________________________________________________________    19.35   18.10   0.8     0.967 4.1%  FIG. 1                                    18.50   17.55   0.6     0.974 3.2%                                            19.00   18.50   0.4     0.987 2.1%                                            21.10   19.75   0.6     0.967 2.8%                                            18.85   18.40   0.9     0.988 4.8%                                            ← mean value →                                                                             0.9766                                                                             3.4%                                            __________________________________________________________________________

Comparative Example 1

The slurry of sample 1-1 prepared in Example 1, the product obtained bydrying this slurry in an electric thermostat drier maintained at 80° C.for 24 hours and the product obtained by calcining this dried product at500° C. for 2 hours were treated with sulfuric acid in an amount of 5moles per mole of the sum of Al₂ O₃ and Na₂ O in the same manner asdescribed in Example 1. In any of these samples, spherical silica couldnot be obtained in a yield higher than 1%.

EXAMPLE 2

A finely divided silicic acid gel obtained by acid-treating acid clayproduced at Nakajo, Niigata Prefecture, Japan, which is a clay of thesmectite group, was prepared as the starting silicate component. Theprocess for the preparation of this silicic acid gel is described below.

It was found that the acid clay produced at Nakajo, Niigata Prefecture,Japan contains 45% by weight of water in the natural state, and the maincomponents are 72.1% by weight of SiO₂, 14.2% by weight of Al₂ O₃, 3.87%by weight of Fe₂ O₃, 3.25% by weight of MgO, 1.06% by weight of CaO and3.15% by weight of the ignition loss based on the dry product (dried at110° C.). This starting acid clay was molded in columns having adiameter of 5 mm and a length of 5 to 20 mm. Then, 1250 kg (as the dryproduct) of the molded clay was charged in a lead-lined wood tank havinga capacity of 5 m³, and 3300 l of an aqueous solution of sulfuric acidhaving a concentration of 47% by weight was added thereto and themixture was heated at 90° C. Thus, the clay was acid-treated in thegranular state for 40 hours, and the sulfate of the basic componentreacted with sulfuric acid was removed by decantation washing using adilute aqueous solution of sulfuric acid and water. Then, the residuewas washed with water until the sulfuric radical was not detected,whereby a granular acid-treated product was obtained.

The results of the analysis of the chemical composition of theacid-treated product after drying at 110° C. for 2 hours are as follows.

Ignition loss (1000° C.×1 hour): 3.75% by weight

SiO₂ : 94.34% by weight

Al₂ O₃ : 1.16% by weight

Fe₂ O₃ : 0.16% by weight

MgO: 0.18% by weight

The concentration of the above-mentioned active silicic acid gel wasadjusted to 20% by weight, and the gel was wet-pulverized by a ball millto obtain the starting silicic acid component.

By using the above-mentioned active silicic acid gel slurry, sodiumaluminate of the reagent grade (Al₂ O₃ =22.5% by weight, Na_(2O=) 15.5%by weight) and sodium hydroxide, a dilute active silicic acid gel slurryand a dilute solution of sodium aluminate were prepared so that theentire amount was 16 kg and the following molar ratios were attained:

Na₂ O/SiO₂ =0.55,

SiO₂ /Al₂ O₃ =6.0, and

H₂ O/Na₂ O=65.

In the same manner as described in Example 1, the crystallization wascarried out and the classification was performed by using a liquidcyclone to obtain a starting material to be subjected to the first stageacid treatment (sample 1-1).

The properties and chemical composition of the so-obtained powder areshown in Table 3. The primary particle size determined by an electronmicroscope was about 1.5 μm, and it was found that the powder wascomposed of spherical particles excellent in the dispersibility.

Then, the powder was subjected to the first stage acid treatment anddried in the same manner as described in Example 1. The properties andchemical composition of the obtained powder (sample 2-2) are shown inTable 3.

The dried powder was calcined at 450° C. for 2 hours and subjected tothe second stage acid treatment by using sulfuric acid in an amount of3.8 or 5 moles per mole of the sum of Al₂ O₃ and Na₂ O in the samemanner as described in Example 1, followed by water washing. An electronmicroscope photo (10,000 magnifications) of the powder (sample 2-3 or2-4) obtained by drying the cake is shown in FIG. 9. The properties andchemical compositions of the powder are shown in Table 3. In the samemanner as described in Example 1, the circularity (A) and notchingdegree (B) were determined from an enlarged photo of 30,000magnifications with respect to five points.

                                      TABLE                                       __________________________________________________________________________    Sample No.           2-1  2-2   2-3   2-4                                     __________________________________________________________________________    Pack density (g/ml)  0.52 0.56  0,54  0.53                                    Specific surface area (BET method) (m.sup.2 /g)                                                    --   38    200   320                                     Oil absorption (ml/100 g)                                                                          50   51    57    62                                      Whiteness (Hunter reflection method) (%)                                                           96.1 96.0  96.4  95.3                                    pH Value of 5% suspension (-/25° C.)                                                        11.20                                                                              8.64  6.7   4.62                                    Particle size (μm) by electron microscope                                                       1.5, truly                                                                         1.2, truly                                                                          1.3, truly                                                                          1.2, truly                                                   spherical                                                                          spherical                                                                           spherical                                                                           spherical                               Crystal form by X-ray diffractometry                                                               Pc form                                                                            amorphous                                                                           amorphous                                                                           amorphous                               Chemical Composition (% by weight)                                            (based on product dried at 110° C.)                                    Ig-loss              11.74                                                                              11.21 7.80  6.90                                    SiO.sub.2            51.18                                                                              56.21 84.8  92.86                                   Al.sub.2 O.sub.3     22.96                                                                              24.88 6.73  0.21                                    Na.sub.2 O           14.02                                                                              7.69  0.61  0.01                                    Total                99.90                                                                              99.99 99,94 99,98                                   SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio                                                            3.79 3.84  12.6  7.52                                    Moisture absorption (% by weight)                                                                  19.7(14.3)                                                                         10.9(5.9)                                                                           12.3(6.4)                                                                           21.3(15.1)                              (90% RH ×24 hours)*1                                                    Yield (%)*2          100  90.8  76.5  58.1                                    Average particle size (D.sub.50) (μm)                                                           1.82 1.67  1.64  1.63                                    __________________________________________________________________________     *1: the parenthesized value indicates the moisture absorption of powder       calcined at 500° C. for 1 hour                                         *2: the yield was calculated from the amount of obtained powder as the        anhydride                                                                

                  TABLE 4                                                         ______________________________________                                        Circularity (A)                                                                            Notching Degree (B)                                                                          Remarks                                           ______________________________________                                        0.981        2.4%           mean value of                                                                 5 points                                          ______________________________________                                    

Comparative Example 2

The slurry of sample 2-1 prepared in Example 2, a product obtained bydrying this slurry in an electric thermostat drier maintained at 80° C.for 24 hours and a product obtained by calcining this dried product at500° C. for 2 hours were subjected to the second stage acid treatment(with sulfuric acid in an amount of 5 moles per mole of Al₂ O₃ and Na₂O) in the same manner as described in Example 1. In any of thesesamples, spherical silica could not be obtained in a yield higher than0.5%.

EXAMPLE 3

P type zeolite was synthesized in the same manner as described inExample 1 except that the synthesis molar ratios were changed asfollows:

Na₂ O/SiO₂ =0.7,

SiO₂ /Al₂ O₃ =8.0, and

H₂ O/Na₂ O=100.

The primary particle size of this zeolite was about 7 μm and it wasfound that the zeolite was composed of spherical particles excellent inthe dispersibility. The properties and chemical composition of thepowder (sample 3-1) are shown in Table 5.

The properties and chemical composition of a product (sample 3-2)obtained by subjected the particles to the first stage acid treatment inthe same manner as described in Example 1 are shown in Table 5. Anelectron microscope photo of a powder (sample 3-3) obtained bysubjecting the above product to the second stage acid treatment is shownin FIG. 10. The properties and chemical composition of the powder areshown in Table 5.

The circularity (A) and notching degree (B) determined in the samemanner as described in Example 1 were 0.989 and 1.8%, respectively.

                                      TABLE 5                                     __________________________________________________________________________    Sample No.           3-1     3-2      3-3                                     __________________________________________________________________________    Pack density (g/ml)  0.87    0.94     0.94                                    Specific surface area (BET method) (m.sup.2 /g)                                                    --      29       303                                     Oil absorption (ml/100 g)                                                                          20      18       20                                      Whiteness (Hunter reflection method)                                                               911.8   94.8     95.2                                    pH Value of 5% suspension (-/25° C.)                                                        10.9    7.9      4.5                                     Particle size (μm) by electron microscope                                                       about 7μ, truly                                                                    about 6.5μ, truly                                                                   about 6μ, truly                                           spherical                                                                             spherical                                                                              spherical                               Crystal form by X-ray diffractometry                                                               Pc form amorphous                                                                              amorphous                               Chemical Composition (% by weight)                                            (based on product dried at 110° C.)                                    Ig-loss              11.00   10.69    81.15                                   SiO.sub.2            52.05   56.21    91.52                                   Al.sub.2 O.sub.3     23.41   25.13    0.37                                    Na.sub.2 O           13.81   7.94     0.01                                    Total                100.27  99.97    100.05                                  SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio                                                            3.78    3.80     421                                     Moisture absorption (L% by weight)                                                                 18.4(13.1)                                                                            10.2(4.1)                                                                              20.96(15.1)                             (90% RH × 24 hours)*1                                                   Yield (%)*2          100     93.7     62.1                                    Average particle size (D.sub.50) (μm)                                                           7.8     7.0      6.7                                     __________________________________________________________________________     Note?                                                                         *1: the parenthesized value indicates the moisture absorption of powder       calcined at 500° C. for 1 hour                                         *2: the yield was calculated from the amount of obtained powder as the        anhydride                                                                

EXAMPLE 4

By using commercially available water glass of the reagent grade (sodiumsilicate No. 3, SiO₂ =27% by weight, Na₂ O=9.0% by weight), sodiumaluminate (Al₂ O₃ =22.5% by weight, Na₂ O=15.5% by weight) and sodiumhydroxide, a dilute solution of sodium silicate and a dilute solution ofsodium aluminate were prepared so that the entire amount was 1.5 kg andthe following molar ratios were attained:

Na₂ O/SiO₂ =0.7,

SiO₂ /Al₂ O₃ =8.0, and

H₂ O/Na₂ O=80.

In a stainless steel vessel having an inner volume of about 2 l, 780 gof a dilute solution of sodium silicate was gradually mixed with 730 gof a dilute solution of sodium aluminate with stirring to obtain asodium aluminosilicate gel which was homogeneous as a whole.

Then, this sodium aluminosilicate gel was charged in a small pressurevessel (Model TEM-U supplied by Taiatsu Glass Kogyo) having an innervolume of about 1.2 l, and the temperature was elevated to 125° C. withstirring and crystallization was effected at this temperature for 6hours. The pressure at this crystallization was about 2 kg/cm² -G. Then,the slurry was taken out from the vessel and the solid was separatedfrom the mother liquid by suction filtration. The solid was sufficientlywashed with water to obtain 120 g of a cake of P type zeolite having asolid concentration of 45% by weight.

The primary particle size of the zeolite by an electron microscope wasabout 1.0 μm. The properties an chemical composition of the powder(sample 4-1) are shown in Table 6.

Then, 50 g of the powder was charged in a beaker having a capacity of 1l and 500 ml of water was added thereto, and 90 ml of sulfuric aciddiluted to 10% by weight was gradually added to the mixture withstirring by a magnetic stirrer. Then, the first stage acid treatment wascarried out in the same manner as described in Example 1 to obtain 40 gof an acid-treated powder (sample 4-2). The properties and chemicalcomposition of the powder are shown in Table 6.

Then, the dry powder was calcined at 450° C. for 2 hours and naturallycooled, and 40 g of the calcined powder was charged in a beaker having acapacity of 1 l and 600 ml of water was added to the powder. The powderwas sufficiently stirred by a magnetic stirrer, and diluted sulfuricacid (50% by weight) was added in an amount of 5 moles per mole of thesum of Al₂ O₃ and Na₂ O in the powder and the treatment was conducted at98° C. for 2 hours.

The post treatment was carried out in the same manner as described inExample 1 to obtain about 20 g of spherical silica particles (sample4-3) having a primary particle size of about 0.8 μm as measured by anelectron microscope.

The electron microscope of the spherical particles is shown in FIG. 11,and the properties and chemical composition of the powder are shown inTable 6.

                                      TABLE 6                                     __________________________________________________________________________    Sample No.           4-1   4-2   4-3                                          __________________________________________________________________________    Pack density (g/ml)  0.43  0.41  0.38                                         Specific surface area (BET method) (m.sup.2 /g)                                                    --    81    320                                          Oil absorption (ml/100 g)                                                                          50    55    61                                           Whiteness (Hunter reflection method) (%)                                                           95.4  95.6  95.1                                         pH Value of 5% suspension (-/25° C.)                                                        11.2  8.8   4.5                                          Particle size (μm) by electron microscope                                                       1.0, truly                                                                          0.8, truly                                                                          0.8, truly                                                        spherical                                                                           spherical                                                                           spherical                                    Crystal form by X-ray diffractometry                                                               Pc form                                                                             amorphous                                                                           amorphous                                    Chemical Composition (% by weight)                                            (based on product dried at 110° C.)                                    Ig-loss              12.13 1045  9.08                                         SiO.sub.2            51.73 56.61 90.72                                        Al.sub.2 O.sub.3     23.00 25.01 0.21                                         Na.sub.2 O           13.88 7.91  0.01                                         Total                100.74                                                                              99.98 100.02                                       SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio                                                            3.82  3.85  734                                          Moisture absorption (% by weight)                                                                  19.0  9.1   23.1                                         (90% RH × 24 hours)*1                                                   Yield (%)*2          100   88.3  51.3                                         Average particle size (D.sub.50) (μm)                                                           1.32  1.30  1.27                                         __________________________________________________________________________     Note                                                                          *1: the parenthesized value indicates the moisture absorption of powder       calcined at 500° C. for 1 hour                                         *2: the yield was calculated from the amount of obtained powder as the        anhydride                                                                

EXAMPLE 5

A beaker having a capacity of 2 l was charged with 100 g of a powderobtained by calcining sample 1-2 obtained in Example 1 at 450° C. for 2hours, and 600 ml of water was added thereto and the powder wasdispersed for 30 minutes with stirring by a magnetic stirrer. Then,hydrochloric acid of the reagent grade (concentration=36% by weight) wasadded in an amount of about 130 ml corresponding to 4 moles per mole ofthe sum of Al₂ O₃ and Na₂ O in the particles, and the temperature waselevated to 95° C. and the treatment was carried out at this temperaturefor 2 hours. Then, the solid was separated from the mother liquor bysuction filtration, washed with water in an amount about 5 times theamount of the mother liquor, dried in an electric thermostat driermaintained at 110° C. for 24 hours and pulverized by a small mill toobtain a powder of spherical silica particles.

Similarly, spherical silica particles were obtained by the treatmentwith hydrochloric acid of the reagent grade in an amount of 6 moles(about 200 ml) or 10 moles per mole of the sum of Al₂ O₃.

The chemical compositions and properties of the obtained powders areshown in Table 7.

                                      TABLE 7                                     __________________________________________________________________________                           4 Moles of Hydro-                                                                       6 Moles of Hydro-                                                                       10 Moles of Hydro-                                        chloric Acid                                                                            chloric Acid                                                                            chloric Acid                       __________________________________________________________________________    Chemical composition                                                                     Ig-loss     13.59     12.43     8.89                               (% by weight) (based                                                                     SiO.sub.2   68.49     86.03     91.06                              on product dried at                                                                      Al.sub.2 O.sub.3                                                                          16.59     1.35      0.03                               110° C.)                                                                          Na.sub.2 O  1.37      0.09      0.00                                          Total       100.04    99.96     99.98                                         SiO.sub.2 /Al.sub.2 O.sub.3                                                               7.02      117       5.160                                         molar ratio                                                        Specific surface are (m.sup.2 /g)(BET method)                                                        168       310       370                                Particle size (μm) by electron microscope                                                         4 truly spherical                                                                       3.8 truly spherical                                                                     3.8 truly spherical                Moisture absorption (%) (90% RH × 24 hours)                                                    12.7      18.9      23.7                               __________________________________________________________________________

EXAMPLE 6

A beaker having a capacity of 500 ml was charged with 50 g of sample 1-3(cake) obtained in Example 1 and 300 ml of water was added thereto, andthe mixture was sufficiently dispersed by a stirrer. A glass electrodeof a pH water was put in the dispersion and the pH value was measured.It was found that the pH value was 4.3

Then, dilute aqueous ammonia having a concentration of 5% by weight wasadded to the dispersion to adjust the pH value to 11 and the treatmentwas conducted at 80° C. for 1 hour.

Then, the solid was recovered by filtration, washed with water, dried inan electric thermostat drier maintained at 110° C. for 24 hours andcalcined at 450° C. for 2 hours. The changes of the specific surfacearea and moisture absorption are shown in Table 8 (sample 6-1).

Sample 2-3 (cake) obtained in Example 2 was treated in the same manneras described in Example 2. The specific surface area and moistureabsorption are shown in Table 8 (sample 6-2).

                  TABLE 8                                                         ______________________________________                                                     Moisture  Specific Surface                                                    Absorption (%)                                                                          Area (m.sup.2 /g)                                      ______________________________________                                        Sample 6-1                                                                    dried product  11.8        120                                                product calcined at                                                                          7.6          81                                                450° C. for 2 hours                                                    Sample 6-2                                                                    dried product  12.9        113                                                product calcined at                                                                          8.5          45                                                450° C. for 2 hours                                                    ______________________________________                                    

Application Example 1

A composition comprising 100 parts by weight of a polypropylene resinhaving a melt flow rate of 1.9 g/10 min, 0.10 part by weight of2,6-di-t-butyl-p-cresol, 0.05 part by weight of calcium stearate and 0.6part by weight of the sample shown in Table 9 was mixed by a super mixerand pelletized at 230° C. Pelletization was carried out in the samemanner as described above by using synthetic silica (0.8 μm) or calciumcarbonate (Eskalon #1500) instead of the sample or without using anyinorganic substance.

The pellets were formed into films by using an extruder and the filmswere drawn at a draw ratio of 6 in each of the longitudinal and lateraldirections to obtain drawn films having a thickness of 30 μm.

With respect to each of the so-obtained biaxially drawn films, thetransparency, blocking property and scratch resistance were determinedaccording to the measurement methods described below. The obtainedresults are shown in Table 9.

(1) Transparency

The transparency was determined according to the method of ASRM D-1003.

(2) Blocking Property

Two films were piled and a load of 20 kg was imposed, and the piledfilms were allowed to stand still in an oven maintained at 40° C. for 24hours. The force necessary for peeling the two films from each other wasmeasured and designated as the blocking property.

(3) Scratch Resistance

Two films were piled and rubbed with fingers. The scratch resistance wasevaluated based on the scratching degree according to the followingscale:

⊚: not scratched at all

◯: slightly scratched

Δ: scratched

X: considerably scratched

Products obtained by calcining samples 1-3, 2-1, 2-2 and 2-3 obtained inExamples 1 and 2 at 400° C. for 1 hour (samples 1 through 4) andproducts obtained by surface-treating calcined samples 2-2 and 2-3(samples 5 and 6) were used at the above-mentioned test.

The surface treatment was carried out in the following manner.

On a watch glass having a diameter of 10 cm, 50 g of the sample wasthinly spread and a silane coupling agent (SH-6040 supplied by ToraySilicone) was sprayed in an amount of about 1% based on the sample by asmall sprayer. Then, the sample was sufficiently stirred and treated inan electric thermostat drier maintained at 150° C. for 3 hours to obtaina surface-treated sample to be tested.

                                      TABLE 9                                     __________________________________________________________________________                                       Blocking                                   Sample             Amount Added                                                                           Transparency                                                                         Property                                                                             Scratch                             No.                (parts by weight)                                                                      (%)    (kg/10 cm.sup.2)                                                                     Resistance                          __________________________________________________________________________    1   Sample 1-3 (400° C. × 1 hour)                                                   0.06     3.7    0.20   ⊚                    2   Sample 2-1 (400° C. × 1 hour)                                                   0.06     4.1    0.25   ◯                       3   Sample 2-2 (400° C. × 1 hour)                                                   0.06     3.8    0.24   ⊚                    4   Sample 2-3 (400° C. × 1 hour)                                                   0.06     3.5    0.21   ⊚                    5   Sample 2-2 (400° C. × 1 hour),                                                  0.06     3.2    0.22   ⊚                        Surface-treated                                                           6   Sample 2-3 (400° C. × 1 hour),                                                  0.06     2.9    0.21   ⊚                        Surface-treated                                                           7   Synthetic silica                                                                             0.06     4.3    0.62   ◯                       8   CaCO.sub.3     0.06     7.8    0.78   X                                   9   not added      0.06     2.0    4.10   ⊚                    __________________________________________________________________________

Application Sample 2

A powder foundation was prepared by using sample 1-3 obtained in Example1.

    ______________________________________                                        Component (A)                                                                 Mica                  38 parts by weight                                      Talc                  10 parts by weight                                      Titanium oxide        18 parts by weight                                      Coloring pigment       5 parts by weight                                      Spherical silica (sample 1-3)                                                                       15 parts by weight                                      Component (B)                                                                 Squalene             5.0 parts by weight                                      Lanoline             4.0 parts by weight                                      Isopropyl myristate  3.0 parts by weight                                      Surface active agent 1.0 part by weight                                       Perfume              appropriate amount                                       ______________________________________                                    

Predetermined amounts of mica, talc, titanium dioxide, coloring pigmentand spherical silica of the component (A) were charged in a stainlesssteel vessel and sufficiently mixed, and the mixture was pulverized byan atomizer. The mixture was sufficiently blended by a Henschel mixer,and a heated mixture of the ingredients of the component (B) was addedand the resulting mixture was sufficiently blended to obtain a product.

The obtained foundation and a foundation free of spherical silica weresubjected to a comparison test by randomly selected twenty adults 20 to50 years old. It was generally judged that the foundation containingspherical silica had a better spreading property and gave a smooth andplain finish and this foundation was excellent in the air permeability.

We claim:
 1. Amorphous silica-alumina spherical particles composed ofX-ray diffractometrically substantially amorphous silica-aluminacontaining less than 25% by weight of Al₂ O₃, and less than 12% byweight of Na₂ O,wherein individual particles have(a) a spherical shapehaving a circularity (A) represented by the following formula: ##EQU7##in which r1 denotes the radius of a circumcircle of said particle and r2denotes the radius of an inscribed circle of said particle, thecircularity (A) being in the range of from 0.90 to 1,(b) a notchedsurface having a notching degree (B) represented by the followingformula: ##EQU8## in which Δt denotes the depth between a peak and atrough in the radial direction of a notch on a cross-section of saidparticle and r1 is as defined above,the notching degree (B) being in therange of from 1 to 10%, and (c) a primary particle size represented bythe formula 2r1, in which r1 is as defined above, in the range of from0.1 to 20 μm, and wherein said particles having a moisture absorptionsmaller than 13% by weight when said particles are held in an atmospheremaintained at a temperature of 25° C. and a relatively humidity of 90%for 24 hours, said particles being obtained by acid-treating zeoliteparticles having an X-ray diffraction pattern inherent to the structureof P zeolite and having a spherical shape and a notched surface toremove the sodium component contained therein.
 2. A filler for apolymer, which comprises amorphous silica-alumina spherical particles asset forth in claim 1 and a resin.
 3. Amorphous silica-alumina sphericalparticles as set forth in claim 1, wherein the standard deviation of theprimary particle size is smaller than 0.85.
 4. Amorphous silica-aluminaspherical particles as set forth in claim 1, wherein the particles havea bulk density of 0.2 to 1.2 g/ml.
 5. Amorphous silica-alumina sphericalparticles as set forth in claim 1, wherein the particles have a BETspecific surface area smaller than 400 m² /g.